Sumaila Safianu put Aizawl FC in the lead in the 30th minute before Alhassan Abubakr equalised for ONGC.
ONGC finished on 22 points from 12 outings.
The second team to qualify for the I-League will be decided when Kolkata's Mohammedan Sporting take on United Sikkim Football Club tomorrow.
A draw for USFC will earn them a ticket to next edition's I-League while Mohammedan Sporting need a win.
